STUDY OF A COMPOUND MICROSCOPE :- FOCUSING OF AN OBJECT and PRECAUTIONS

Microscope

FOCUSING OF AN OBJECT

A. Under Low Power :-

1.    Place the slide to be focused the stage and fit it into the mechanical stage. By means of the screw of the mechanical stage bring the object on the central aperture in the stage.

2.    Using the light source and by adjusting the plane mirror, focus the light on the object. Partially close the iris diaphragm and lower the objective (10x) with coarse adjustment near the slide.

3.    The position of the slide is so adjusted that the aperture of the objective lens is just above the point to be focused on the slide.

4.    Now look into the eye – piece ; the optical tube is moved upwards (again using coarse adjustment ) slowly and confidently, till the object comes under view. Once this is achieved , the coarse adjustment should Not be used.

5.    Lower the condenser from the top position till the object is properly illuminated. The condenser usually occupies a low position.

6.    Next , using the fine adjustment only, the slide can be brought to a sharp focus.

LOW POWER LENS

Important Note :- Always keep looking from the side of the microscope as you are lowering the optical tube, otherwise you are liable to damage the slide.

B.    Under High Power :-

1.    For focusing under high power (40x) , simply rotate the nose – piece so that the high    power objective lens may come to lie above the slide to a sharp focus.

2.    The iris diaphragm is fully opened and concave mirror is used to condense the light on the   object.

3.    The condenser is kept in the beginning at the top and is then gradually lowered till the    object is properly illuminated. The condenser usually occupies a higher position than    that for focusing under the low power.

4.    With the fine adjustment screw, attempt the final focusing.

HIGH POWER LENS

      C.   Under Oil Immersion Lens :-

1.    For focusing under oil immersion lens (100x), a drop of cedar – wood oil is placed on the slide. Then turn the nose piece further so that the oil immersion lens may be in use. It will automatically dip into the drop of oil.

2.    As the slide is moved, the drop of oil will also get moved on its own. Thus any part of the slide can be observed.

3.    The iris diaphragm is kept fully opened and the condenser is kept in the top position. Use only the fine adjustment to focus the necessary area.

100X LENS   AND  CEDAR WOODEN OIL

Important Note:- While putting the stained slide, care should be taken so that the stained smear may be facing the objective.

Important Points to Remember

1.          Position of Condenser :- The Desired position of the condenser is as follows :-

Objective Lens Power	Condenser Position
(i)  Low Power (10x)	(i) Lowest
(ii) High Power (40x)	(i) Higher (in between i and iii)
(i) Oil Immersion (100x)	(i) Highest

1.          Type of Mirror to be used

(i)  The Plane side of the Mirror is used when:-

      (a) A condenser is used ;

      (b) The source of light is diffuse such a daylight.

(ii)  Concave mirror is used when source of light is from a point source such as bulb, as   used in labs.

2.          The Higher the Magnification, the smaller the area that can be examined at a time. Therefore, to start with, irrespective of what is being examined, it is always advisable to focus a slide under low power (10x) first. Obtain a general view of the object and choose the field you would like to examine in detail. Bring this field in the central position. Then switch over to the next high power. Now use only the fine adjustment for focusing. If necessary, select the field further and bring it in the centre again.

Most Important Part of Microscopy

PRECAUTIONS

1.       A clear image can never be seen through dirty lenses. Make sure that the eye piece as well as all the objectives is clean.

While cleaning microscope lenses, do not rub them with dry cotton or rough cloth which might leave permanent scratch marks on the lenses. Apply xylene  to the lenses (to dissolve the grease) and then wipe dry gently with a piece of silk cloth or softest material available.

Most Important NOTE :- Always clean the Microscope lenses BEFORE and AFTER the use.

2.       Do not clean the objective with alcohol, as it may dissolve the cement which unites the component lenses.

3.       Never lower the optical tube while you are looking through the eye piece.

4.       Make minimal and careful use of ONLY the fine adjustment while using the high power and oil immersion.

5.       If the microscope has to be moved, it should be held upright by the limb keeping a hand below its foot.